Event when all mdi forms are closed - forms

Question

Guys, I'd like if anyone knows any event or method that I can intercept when all MDI forms were closed.
Example:
I want to implement an event in my main form where when I close all MDI forms, such an event was triggered.
Grateful if anyone can help.

Answer 1

MDI child forms (in fact any form), while being destroyed, will notify the main form. You can use this notification mechanism. Example:
type
TForm1 = class(TForm)
..
protected
procedure Notification(AComponent: TComponent; Operation: TOperation);
override;
..
procedure TForm1.Notification(AComponent: TComponent; Operation: TOperation);
begin
inherited;
if (Operation = opRemove) and (AComponent is TForm) and
(TForm(AComponent).FormStyle = fsMDIChild) and
(MDIChildCount = 0) then begin
// do work
end;
end;

Answer 2

Catch the WM_MDIDESTROY message send to the MDI client window:
type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
FOldClientWndProc: TFarProc;
procedure NewClientWndProc(var Message: TMessage);
end;
...
procedure TForm1.FormCreate(Sender: TObject);
begin
if FormStyle = fsMDIForm then
begin
HandleNeeded;
FOldClientWndProc := Pointer(GetWindowLong(ClientHandle, GWL_WNDPROC));
SetWindowLong(ClientHandle, GWL_WNDPROC,
Integer(MakeObjectInstance(NewClientWndProc)));
end;
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
SetWindowLong(ClientHandle, GWL_WNDPROC, Integer(FOldClientWndProc));
end;
procedure TForm1.NewClientWndProc(var Message: TMessage);
begin
if Message.Msg = WM_MDIDESTROY then
if MDIChildCount = 1 then
// do work
with Message do
Result := CallWindowProc(FOldClientWndProc, ClientHandle, Msg, WParam,
LParam);
end;

Answer 3

You can have the MainForm assign an OnClose or OnDestroy event handler to each MDI child it creates. Each time an MDI client is closed/destroyed, the handler can check if any more MDI child forms are still open, and if not then do whatever it needs to do.
procedure TMainForm.ChildClosed(Sender: TObject; var Action: TCloseAction);
begin
Action := caFree;
// the child being closed is still in the MDIChild list as it has not been freed yet...
if MDIChildCount = 1 then
begin
// do work
end;
end;
Or:
const
APPWM_CHECK_MDI_CHILDREN = WM_APP + 1;
procedure TMainForm.ChildDestroyed(Sender: TObject);
begin
PostMessage(Handle, APPWM_CHECK_MDI_CHILDREN, 0, 0);
end;
procedure TMainForm.WndProc(var Message: TMessage);
begin
if Message.Msg = APPWM_CHECK_MDI_CHILDREN then
begin
if MDIChildCount = 0 then
begin
// do work
end;
Exit;
end;
inherited;
end;